Tire Pressure Monitoring Systems (TPMS) are designed to monitor the air pressure inside of pneumatic tires on various types of vehicles. Therefore pressure sensors are used in the tires and the system may report the tire pressure information to the driver of the vehicle. Wireless transmission can be used to transmit information on the pressure data to a centralized receiver component in the vehicle. Such a configuration can enable the system to report or signal pressure losses of the tires to the driver. Some known TPMS provide localization information on the tire or wheel on top of pressure information so as to indicate to a driver of a vehicle the position of a wheel having a pressure loss. Examples are indications on whether a pressure loss of a tire of a wheel of a car is on the Front Left (FL) tire, the Front Right (FR) tire, the Rear Left (RL) tire, and/or the Rear Right (RR) tire. After replacement of a wheel or tire, assignment or re-assignment of the sensor signals to the positions on the vehicle may be necessary. Such assignment can be carried out manually, for example, by using a Low-Frequency (LF) initializer, which is used to initialize each individual sensor upon indication from a system receiver. The initialization can be affected by sequentially activating an LF-initiator in the proximity of the respective sensor and receiving an according response with a unique identification from the sensor.
Some known TPMS systems utilize multiple LF-initializers, e.g. in terms of transmitter coils or inductors, for initialization of each individual sensor or wheel, for example, they can be mounted in the wheel housing of each wheel. The number of involved LF-initializers may render such an approach uneconomic. For example, an identification of the sensor may then be assigned to an initialized position on the vehicle, which assumes that the according initialization procedure is carried out correctly after a change of tires, replacement of a wheel, etc. Other concepts make use of different reception levels of the LF-radio signals using transmitter coils at different locations asymmetric to the wheels, e.g. one in the front and one in the back. These concepts are extensive and unsuitable for after-market installation. Further concepts make use of the varying reception power of the RF-signals transmitted by the sensors. The reception power of such an RF-signal can be measured and the different locations can be distinguished by the different reception levels, e.g. evoked by different distances of the wheels. The larger the distance between a wheel and the corresponding receiver the lower the reception power. In some cars a distinction between the signals from the front and the signals from the back is possible, as the receiver is located at an asymmetric position i.e. close to a rear axis, a distinction between signals from the left and right is rather difficult. Some concepts may use a set of acceleration sensors, which are installed in an orthogonal manner in each wheel to determine the rotational direction of the wheels to distinguish left and right wheels. This concept may suffer from the complex propagation paths of the wireless signals, which may render an assignment of a reception level of a signal to a certain wheel difficult.
Another concept uses ABS (Anti-lock Braking System) signals to determine rotational frequencies of the wheels and relate or correlate them to rotational frequencies determined based on TPMS signals, which may make use of acceleration sensors determining the acceleration changes as the sensor rotates with the wheel in gravitation. This concept, however, may be difficult to establish if the signals of the ABS system cannot be made available. This may render the concept unsuitable for after-market systems.